Method of treating coal



Patented June 6, 1933 UNITED STATES PATENT OFFICE HARVEY R. FIFE, 'OFPITTSBURGH, PENNSYLVANIA METHOD OF TREATING GOAL No Drawing.

combustion, particularly if there is present with the coal a substantialquantity of dust therefrom. As is well known, this dust will also forman explosive mixture with the oxygen of the atmosphere. A previouslyknown method of'laying coal dust is to spray the coal in bulk with asolution of an inorganic substance, such as calcium chloride, andthereby form a coating over the lump coal and the dust therefrom.

The method of my present invention is particularly valuable for use withlump coal.

I have discovered that an effective and economical method of protectingthe coal from deterioration and oxidation, is to cover the surface ofthe coal with a. thin adherent coating or tegument of a combustible andviscous substance. As such coating substance I prefer waxes and lowmelting tars or asphalts. It is necessary that the coating or tegumentbe viscousin order that it may seal the coal within a suitable envelope,in order that it may solidify on the surface of the coal, and in orderthat the ignition temperature of the coal may not be materiallyaffected. For these reasons the coating material should be applied in ahighly fluid condition, its viscosity being lower than the normalviscosity of the coating substance at room temperature. This fluiditymay be obtained by means of a suitably applied temperature sufficientlyhigh to secure fluidity of the coating material.

One mode of, application, which I have employedsuccessfully, is to dipthe coal by suitable means, such as' a belt conveyor in a bath of meltedparatlin wax. The coal'is introduccd at room temperatures, so that thewax tends to congeal on the individual lumps and particles of coal.

The coal so coated is then removed. from the bath and is subjected to aflowing step,

Application filed June 25, 1930. Serial Noi 463,838.

which consists in subjecting the coal to a higher temperature,materially above the melting point of the wax. The step causes the waxto so flow over the entire surface of each lump or particle of coal thatupon congelation it provides a thin, sealed, coating or tegument ofsemi-solid material on each lump or particle.

When the coal is dipped in melted wax, the

flowing step is essential in order that the coating on the coal may bethin and continuous to form the desired sea-l.

Another mode of applying the coating, by means of a heated bath,consists in utilizmg parafiin wax, orlother suitable coating material,in a suspension, or mechanical mixture, with heated water. Assuming thatparaffin wax is used, a bath may be prepared by raising the water to atemperature mate rially above the melting point of the particular waxwhich is to be applied to the coal. The melting point of the wax usedwill vary considerably with different runs inasmuch as it is desirable,for reasons of economy, to use unrefined wax obtained as a residue fromthe distillation of paraflin base petroleum; but in any case thetemperature of the bath, as noted above, should be materially higherthan the melting point of the wax, in order that it may flow readily andadhere to the coal in semi-solid state, as a uniform coating, in orderto seal the lumps or particles of coal. I

With suspension, or mechanical mixture, of melted wax and water, thecoal is dipped in the bath and may be rapidly removed therefrom. As atypical example a bath is prepared by adding 1 to 5% by weight ofparaffin wax to the water and raising the temperature of the water bythe application of heat in any suitable manner. I have found that thistemperature should be at least 5 degrees centigrade above ,the meltingpoint of the coating material, and may desirably in some instances be ashigh as 50 degrees Centigrade above the melting point. In general Ihave, found satisfactory a temperature .of 20 degrees centigradc higherthan the melting point of the wax, or other coating material, used. Thecoal is then passed through the its concentration with respect to thewax suspended in the water thereof, and the duration of the dippingstep. The coal as.

19 passed through the bath is substantially at room temperature and thedeposition of the wax is, therefore, rapid if. the temperature of thebath is sufficiently high. Avoidance of a coating which may be so thickas tobe wasteful or so thick that it will remain objectionahly sticky ortacky upon solidification, is avoided both by an adequately high bathtemperature, hy the inclusion of a relatively small quantity of wax inthe bath with respect to the suspending liquid, and by an adequateperiod of immersion.

I have obtained good results by preparing a bath containing water andparaffin wax, the wax being added in a proportion of three per cent. byweight and raising the temperature of the bath to 65 degrees centigrade.I then dipped the coal in the bath while subjecting the bath to rapidmechanical agitation and removed it therefrom after an immersion of afew seconds. Lumps of coal, having a relatively great surface area withrespect to their weight were covered with a sealed coating of wax theweight of which was .7 or less the weight of the coal.

Instead of dipping the coal in a bath, a suspension may be prepared byagitating the wax with water while heating the mixture to form thesuspension, and spraying the mixture of water and wax on the coal whichis to be coated. In so applying the coating Wax to the coal, it isnecessary to exercise care to assure the high temperature of themechanical mixture of wax and water at the instant of its physicalcontact with the coal.

45 Various alternative substances may be used in place of the paraffinwax. For example, I have used neutral pitch and neutral a-sphalts, whichlatter may be either neutral asphalts of natural occurrence or neutrala'sphalts resulting as a still residue.

In utilizing any of these substances I have found it important that theybe so produced or treated that they are in neutral, rather than acid,condition. This is for the reason that the coating material should forma mechani al mixture with the water, rather than an emulsion therewith.In using an emulsion there is a tendency for the material depositedtherefrom to gather in lumps or globules on the surface of the coal,rather than'to spread thereover in the desired thin and adherentcoating-to form an individual seal for each lump or particle of coal.

It should be understood that in using pitch, asphalt, rather thanparaffin wax, as a coating material, the same general mode ofapplication may be employed and the same factors are of importance. Itis important that the tar or asphalt be mixed with the carrying liquidin a relatively small proportion; that the temperature of the liquid bematerially higher than the melting point of the tar or asphalt; and, ifthe coal be dipped, that the period of immersion be of sufficientduration 'and the secondary flowing step be at a high temperature, tosecure an adequate flowing of the tar or asphalt to produce the desiredthin, sealed, coating.

It may be noted that the application of the coating material by amechanical mixture of the coating material with a carrying liquidrequires no flowing step, the flowing effect being obtained in the bathitself or by the dispersion of a spray applied at a high temperature.

It should be understood that while water has been mentioned, othercarrying liquids may be employed if so desired. Insofar as this mannerof conducting the method is concerned, the requisite qualities of thecarrying liquid are that it have a relatively high boiling point, sothat the desired high temperature of the suspension may be attained, andthat it is a liquid in which the coating material is insoluble orsparingly soluble. It should be further understood that a mixed coatingmaterial, as for example a mixture of paraffin wax and asphalt, may beemployed if the temperature of the suspension is materially higher thanthe melting point of the mixture.

It may be generally noted that my method provides the coal with acoating so thin that it does not increase the fire hazard by appliedflame while decreasing the fire hazard from spontaneous combustion. Thecoating is also so thin that there is no marked tendency towardagglomeration of the lumps or particles of the coal in handling andshipping, such as would be the case if a relatively thick coating ofobjectionably sticky material were applied to the individual lumps orparticles.

My method thus differs widely from previous methods in which the objecthas been to cause the agglomeration of fine particles of coal, or othercombustible solid, with a viscous substance which may be added in arelatively great proportionate quantity, to form a mixed mass with thesolid fuel particles.

What I claim is:

1. The method of protecting coal from dusting and oxidation whichcomprises subparticles in a thin-film, and permitting the wax to congealduring cooling to normal room temperature to form a thin sealed coatingof semisolid material on each individual and unag lomerated particle.

2. The method of protecting coal from dusting and oxidation whichcomprises sub- -jecting the coal to a bath containing paraffin wax inliquid suspension, the temperature of the bath being materially higherthan the melting point of the wax to flow the wax over the entiresurface of the individual coal particles in a thin film, and permittingthe wax to congeal during cooling to normal room temperature to form athin sealed coat- I ing on each individual and unagglomerated particle.I

3. The method of protecting coal from dusting and oxidation whichcomprises subjecting the coal to a bath containing paraffin wax inliquid suspension, the wax being present in a proportion of from one percent. to five per cent. the weight of the liquid, raising thetemperature of the bath to a point materially higher than the meltingpoint of the wax to flow the wax over the entire surface of theindividual coal particles in a thin film, and permittingthe wax tocongeal during cooling to normal room temperature to form a thin sealedcoating of semisolid material on each individual and un'agglomeratedparticle. i

4. The method of protecting coal from dusting and oxidation whichcomprises subjectingthe coal to a bath containing in a carrying liquid amixture of paraiiin waX with another viscous hydrocarbon which issemisolid at normal room temperature, the coating mixture being presentin a proportion of from one per cent. to five per cent. the weight ofthe liquid, raising the temperature of the bath to a point materiallyhigher than the melting point of the coating mixture to flow the coatingmixture over the entire surface of the individual coal particles in athin film, and permitting the coating mixture to congeal during coolingto normal room temperature to form a thin sealed coating on eachindividual and unagglomerated particle.

5. The method of protecting coal from dusting and oxidation whichcomprises subjecting the coal to a bath containing paraflin wax in acarrying liquid, the temperature of present in the proportion of fromone per film, and permitting the wax to congeal during cooling to normalroom temperature to form a thin sealed coating of semisolid material oneach individual and unagglomerated particle.

7.-The method of protecting coal from dusting and oxidation whichcomprises subjecting the coal to a bath containing in a carrying liquida mixture of p-arafiin wax with another viscous and neutral hydrocarbonwhich is semisolid at normal room temperature, raising the temperatureof the bath to a point materially higher than the melting point of thecoating mixture to flow the coating mixture over the entire surface ofthe individual coal particles in a thin film, and permitting the coatingmixture to congeal during cooling to normal room temperature to form athin sealed coating on each individual and unagglomerated particle.

8. The method of protecting coal from dusting and oxidation whichcomprises subjecting the coal to a bath containing in liquid suspensiona coating material consisting wholly of viscous and neutral organicingredients which are semisolid at room temperature, raising thetemperature of'the bath to a point materially higher than the melting.

point of that ingredient of the coating material having the highestmelting point to flow the coating material over the entire surface ofthe individual coal particles in a thin film, and permitting the coatingmaterial to congeal during cooling to normal room temperature to form athin and uniform sealed coating on each individual and unagglomeratedparticle.

In testimony whereof I have hereunto set my'hand.

. HARVEY R. FIFE.

the bath being materially higher than the melting point of the wax toflow the wax over the entire surface of the individual coal partlcles ina thin film, and permitting the wax to congeal during cooling to normal"

